Capacitive imaging devices using an array of M row electrodes and N column electrodes are competing with devices using a grid of M by N electrodes connected to a processing circuit through M times N connecting lines, or through a minimum of M times N active elements such as field effect transistors. An array of M row and N column electrodes, though, can be implemented on any substrate and only requires M plus N connections for sensing the M times N row-to-column mutual or cross-capacitances concentrated near row-to-column crossovers.
State-of-the-art capacitive imaging devices using an array of row and column electrodes sense cross-capacitances by one electrode set (rows or columns) operating as drivers coupling to the other electrode set operating as pickups, as disclosed in U.S. Pat. No. 7,663,607 (Hotelling et al.), specifically in FIG. 9 and related text. To keep the measurement unaffected by pickup electrode capacitive loading, a charge amplifier (an operational amplifier with capacitive feedback from output to inverting input) can be inserted, as disclosed in FIG. 13 and related text.
However, cross-capacitance coupling from a drive electrode to a pickup electrode only takes place near their crossover, while interfering signals from voltage sources such as AC lines may couple to a substantial part of the pickup line, adding noise to the measurements.
As disclosed in an embodiment of U.S. Pat. No. 8,654,098 (Ningrat) a measurement of the column electrodes' self-capacitance is combined with the aforementioned row-to-column cross-capacitance measurement, and both data sets combined to reduce the effect of noise. This more complex approach only works for touch detection, though.
For hidden object detectors, the capacitive image is best displayed to the user by a display right over or near the capacitive electrode array. The two next patents are only mentioned here for their capacitive image display, neither of them disclosing row and column electrodes. U.S. Pat. No. 8,476,912 (Dorrough) discloses a stud sensor having a linear array of electrodes covered by a linear array of LEDs, letting the user “see” the studs along the line. U.S. Pat. No. 9,103,929 (Krapf et al.) discloses a planar array of individually addressable electrodes or pixels, covered by a planar array of display points, letting the user “see” the hidden objects. Imaging and display arrays of similar size create the illusion of a “window” through which hidden objects can be “seen”, helping users to identify hidden objects.